The present invention relates generally to lasers and particularly to upconversion lasers, sum frequency generation, optical waveguides, and waveguide lasers.
Upconversion lasers are among the most efficient sources of coherent visible and near-ultraviolet radiation. The term xe2x80x9cupconversionxe2x80x9d is well known in the art and generally refers to emission of optical energy having a frequency that exceeds that of the pumping frequency.
One way to convert fundamental infrared emission to visible light relies on non-linear optical techniques such as harmonic generation or optical parametric oscillation. Most solid state lasers produce fundamental radiation in the infrared. For example Nd:YAG is a trivalent neodymium ion-doped solid state laser which operates at several infrared wavelengths including 1.06 xcexcm and 1.3 xcexcm. Another common solid state laser is Ti:sapphire, a commercially available trivalent transition ion-doped tunable laser with a peak emission wavelength at approximately 780 nm.
Crystalline upconversion laser gain elements typically contain a trivalent rare earth ion doped in a suitable oxide or fluoride host crystal. An upconversion laser gain element differs from traditional gain elements in that the activator ion doping concentration is relatively high. However, some crystal hosts and activator ions that produce efficient traditional (non-upconversion) laser-emission are not capable of producing upconversion laser emission.
Most demonstrations of upconversion laser emission have taken place in fluoride hosts. The fluoride host is preferred because its low phonon frequencies produce long lifetimes for the metastable states involved in the upconversion process.
Few demonstrations of upconversion laser emission in oxide-containing crystal hosts are known. The trivalent rare earth ions (or activator ions) that have demonstrated upconversion laser emission are Pr3+, Nd3+, Ho3+, Er3+, and Tm3+. Upconversion laser emission is known in a non-halide-containing crystal of Tm:YAG at a wavelength of 486 nm. YAG is an oxide containing garnet structure with a chemical formula Y3Al5O12. In addition, Er:YAG has produced upconversion laser emission at 561 nm. The power output of these gain elements is relatively low compared to the levels required for many application.
Er:YALO denotes an yttrium orthoaluminate crystal doped with trivalent erbium ions. YALO is an acronym for a crystal with the chemical formula YAlO3. The proper name for this crystal is yttrium orthoaluminate. The crystal is commonly referred to as YALO, or alternatively, YAP. The xe2x80x9cPxe2x80x9d stands for perovskite. There are numerous difficulties that must be overcome to produce efficient-upconversion in an oxide-containing crystalline host such as YALO or YAG. A motivation for overcoming these difficulties is that a solid state upconversion laser may be used in generating laser radiation at ultraviolet frequencies useful for semiconductor manufacturing applications, particulary if the ultraviolet radiation may be modulated.
A continuing need therefore exists for a solid state ultraviolet laser capable of being modulated.
A solid state modulated ultraviolet laser of the present invention comprises a laser diode for generating modulated optical energy, a waveguide upconversion laser for converting a portion of the modulated optical energy to upconversion optical energy, and a waveguide sum frequency generator for combining the modulated optical energy and the upconversion optical energy to generate a modulated ultraviolet signal.
An advantage of the solid state modulated ultraviolet laser of the present invention is that the optical conversion efficiency is higher than that of conventional photon avalanche upconversion lasers.
Another advantage is that the ultraviolet output may be modulated up to gigahertz rates by the electrical signal applied to the laser diode.